System for purging a device

Abstract

A system for purging a device for injecting fuel into an exhaust system of an engine comprising a device having an input and an output coupled to an exhaust system, at least one air valve and at least one fuel valve. The air valve has an input an input coupled to an air supply and an output coupled to the device through a check valve. The fuel valve has an input coupled to a fuel supply and an output coupled to the device through a check valve. When the air valve is open and the fuel valve is closed, air flows from the air supply to the device and is injected into the exhaust system of the engine. When the air valve is closed and the fuel valve is open, fuel flows from the fuel supply to the device and is injected into the exhaust system of the engine.

What is claimed is: 
     
       1. A system for purging orifice clogging due to coking of a device for injecting fuel into an exhaust system of an engine comprising:
 a device for injecting fuel into the exhaust system having an input, and an output coupled to an exhaust system; 
 a first air valve having an input and an output; 
 a second air valve having an input coupled to the output of the first air valve and an output coupled to the device through a first check valve; 
 a volume coupled to the output of the first air valve and the input of the second air valve; 
 at least one fuel valve separate from the at least one air valve, having an input coupled to a fuel supply and an output coupled to the device through a second check valve; and 
 an air control valve having an inlet coupled to an air supply and an output coupled to the at least one fuel valve, the first air valve and the second air valve, wherein the air control valve uses air to actuate the at least one of first air valve, the second air valve, and the fuel valve; 
 wherein when the first air valve is closed, the second air valve is open and the at least one fuel valve is closed, air flows from the volume to the device and is injected into the exhaust system of the engine through the output of the device; 
 wherein when the second air valve is closed and the at least one fuel valve is open, fuel flows from the fuel supply to the device and is injected into the exhaust system of the engine through the output of the device. 
 
     
     
       2. The system of  claim 1 , wherein the device is a doser valve. 
     
     
       3. The system of  claim 1 , wherein the device is a nozzle in the exhaust system of the engine. 
     
     
       4. The system of  claim 1 , wherein pressure of the air supply is regulated. 
     
     
       5. The system of  claim 1 , wherein pressure of the fuel supply is regulated. 
     
     
       6. The system of  claim 1 , wherein the at least one air valve and the at least one fuel valve are controlled by a solenoid. 
     
     
       7. The system of  claim 1 , wherein when the first air valve is open, the second air valve is closed, and the fuel valve is open, air from the air supply flows into the volume.